I'm a little confused. These users are paying for the app and then leaving reviews to complain about having to pay (and maybe refunding afterwards)? Or they review the free version of a paid app to complain about the price of the paid app?
Basically some free users when presented with “you need to upgrade to use this” will leave a bad review. And that is 100% logical: some users believe that all online software should be free. And they never pay for software at all (since their company or school pays, etc. - but they don’t).